Head-up display (HUD) systems are currently used in aircraft to provide pilots with essential information superimposed onto their forward field of view through the aircraft windshield. The information displayed is typically data or symbolic images indicative of flight conditions, such as the operating condition of the aircraft, environmental information, or guidance information. HUD systems are also being designed for use in automobiles and other vehicles.
In one type of aircraft HUD system, a light source emits a colored image carried by multiple wavelengths of light in response to signals generated by an image signal controller. The light rays carrying the colored image propagate through a relay lens to create an intermediate image. A wavelength selective combiner reflects the intermediate image toward a pilot, who views the image as it is superimposed on an outside world scene in the same field of view. The combiner is constructed to have multiple optical powers that correct for longitudinal color aberrations introduced by monochromatic relay lens elements and thereby presents to the pilot a correctly focused multi-colored final virtual image at or near optical infinity. The design details of a multi-color HUD system are described in U.S. Pat. No. 5,710,668, which is assigned to the assignee of this patent application.
Guidance information displayed on a HUD combiner for observation by a pilot frequently includes symbology that represents position and attitude guidance for the aircraft during flight. One example is a flare anticipation cue implemented in a Flight Dynamics Head-Up Guidance System (HGS) that is certified by the Federal Aviation Administration for use on Boeing 737-300 aircraft. The flare anticipation cue alerts the pilot several seconds before the aircraft reaches a flare initiation height and indicates to the pilot the pitch up rate required at the initial part of the flare. Another example is a turn anticipation cue that is described in co-pending International Patent Application No. PCT/US98/14177, which is assigned to the assignee of this application. The turn anticipation cue provides guidance information to a pilot during low visibility ground weather conditions after the aircraft has touched down so that the pilot can safely taxi the aircraft to the airport terminal.
Most current aircraft cockpit displays of basic flight information provide no indication of the acceleration or deceleration of the aircraft. The above-noted HGS provides such an indication in a gross qualitative format, informing the pilot only that the aircraft is decelerating a little or a lot as it moves on the ground. There is provided no reference that allows quick-glance interpretation of the deceleration with respect to any reference familiar to the pilot. The lack of a direct indication of deceleration with respect to a known reference makes it difficult for the pilot to determine the actual deceleration of the airplane (as opposed to commanded or expected deceleration) during aircraft landing rollout or rejected takeoff (RTO). Whenever the actual deceleration is less than the nominal or expected deceleration, caused, for example, by wet or icy runway surface conditions, a consequence can be delayed pilot recognition of inadequate deceleration. This can lead during aircraft rollout to delayed action in establishing the necessary deceleration to stop the aircraft on the remaining runway surface or during landing to delayed recognition of a need to initiate a go-around maneuver. In either situation, without good indication of the actual deceleration, the chances of a runway excursion are increased.
It would be desirable, therefore, to provide for display to a pilot a quantitative indication of the deceleration of the aircraft during landing rollout or rejected takeoff.